Un modèle micromécanique pour la nucléation de fissures en fatigue polycyclique

A multiscale approach of multiaxial fatigue in unlimited endurance is proposed. It allows to take into account coupled plasticity and damage mechanisms which occur at the scale of Persistent Slip Bands (PSB). The damage is modelled as the consequence of microvoids growth along PSBs. The proposed macroscopic fatigue criterion, which corresponds to microcracks nucleation at the PSB-matrix interface, is derived by using Kröner homogenization scheme. The role of a mean stress and of the hydrostatic pressure in high cycle fatigue is shown. This dependence is related to the damage micro-mechanisms. Finally, some illustration concerning the particular case of affine loadings is presented. Comparisons of the obtained criterion with experimental data shown the relevance of the approach.